The eastern seaboard of the U.S., already waterlogged from several days of heavy rain, can expect even more over the next week. A combination of an upper level low pressure area over the deep south and Hurricane Joaquin (now pummeling the Bahamas) are combining to send a non-stop stream of moisture laden air up the east coast.
As of late Thursday evening the forecast path of Category 4 Hurricane Joaquin was still up in the air, although most models are now keeping the storm offshore from the U.S. east coast as it heads north. If this turns out to be the case, the east coast will be spared the very strong winds and large storm surge that would accompany the storm, but flooding rains are still expected.
This plot, taken from the U.S. global numerical weather prediction model, the GFS, shows rainfall expected over the next 6 days for North America. Some of the forecast amounts are quite astonishing, the entire state of South Carolina is forecast to have over 5 inches of rain, with most of the state expected to see between 10 and 15 inches, with some of the higher elevations getting up to 20 inches! Pretty much the entire east coast should be wet, but the heaviest stuff is concentrated from northern Georgia to Virginia.
Of course, this will be dependent on the exact track of Hurricane Joaquin. If the storm tracks closer to land, the high precipitation areas will extend farther north, perhaps into Long Island and New England.